Accumulating evidence incriminates environmental pollutants as a significant cause of endocrine disruption involving ovarian toxicity. Dioxins like TCDD are potent reproductive toxicants known to affect steroid levels in laboratory animals and humans. This proposal expands previous studies by this group into mechanisms of action of TCDD. Recent results from human granulosa lutein cell culture (hGLCC) have demonstrated that TCDD has differential effects on hormone secretion through distinct significant transduction pathways that induce -post-translational modifications of specific enzymes expressed in hGLCC. Our studies of the effect of TCDD on steroidogenesis have been significantly expanded and how include studies on TCDD effects on not only utilization of steroid substrates involved in steroid synthesis, but also investigations on P450 and reductase components of 17a hydroxylase /17,20-lyase enzyme complex and the availability of reducing equivalents to support estrogen synthesis. These studies will identify molecular lesions leading to inhibition of estrogen synthesis that accompany fetal loss after in vivo TCDD exposure. We will compare in vitro and in vivo effects of dioxins on ovarian cell function by obtaining ovarian cells from macaques treated in vivo with TCDD in Project II. These cells will be used to validate that the specific perturbations in cellular functions demonstrated in the in vitro studies are also present in cells from in vivo treated animals. Since our results show that TCDD also alters the amounts of bioactive and immunoreactive hCG produced by trophoblasts in vivo and in vitro, we will further characterize how altered isoforms of hCG induced by TCDD affect hGLCC function. Finally, studies will be extended to include follicular phase ovarian cells in primates, based on the TCDD inhibition of 17,20-lyase activity in vitro. These combined experiments should produce a comprehensive understanding of the mechanism of action of dioxin on primate ovarian function associated with infertility and early fetal loss.